Some transmission type image display apparatuses such as liquid crystal display apparatuses use a direct surface light source device as a backlight. In recent years, direct surface light source devices having a plurality of light emitting elements as the light source have been used.
For example, a direct surface light source device includes a substrate, a plurality of light emitting elements, a plurality of light flux controlling members and a light diffusion member. The light emitting elements are disposed on the substrate in a matrix. A light flux controlling member configured to expand the light emitted from each light emitting element in the surface direction of the substrate is disposed above each light emitting element. The light emitted from the light flux controlling member is diffused by the light diffusion member so as to illuminate a member to be illuminated (for example, a liquid crystal panel) in a planar fashion (see, for example, PTL 1).
The surface light source device disclosed in PTL 1 includes a housing, a substrate disposed in the housing, a light emitting element disposed on the substrate, a light flux controlling member disposed on the substrate to cover the light emitting element and to control the distribution of the light emitted from the light emitting element (light direction conversion optical device), and a light diffusion member (diffusion transmission section) configured to allow the light emitted from the light flux controlling member to pass therethrough while diffusing the light. The light flux controlling member includes an incidence surface on which the light emitted from the light emitting element is incident, a reflection surface formed on the side opposite to the incidence surface and configured to reflect the incident light in the lateral direction, and an emission surface configured to emit the light reflected by the reflection surface.
The light emitted from the light emitting element is incident on the light flux controlling member from the incidence surface. The light incident on the light flux controlling member is laterally reflected by the reflection surface, and emitted to the outside of the light flux controlling member from the emission surface.